Polysialo synthesis

H. Ishida, Y. Ohta, Y. Tsukada, M. Kiso, and A. Hasegawa, A synthetic approach to polysialo-gangliosides containing a-sialyl-(2— 8) sialic acid Total synthesis of ganglioside GD3, Carbohydr. Res. 246 15 (1993). 

Synthesis of Polysialo Ganglio-Series Gangliosides 313 12.3.1 Retrosynthetic Analysis of GQlb... 

GD2 pentasaccharide acceptor 14 was selected as the key compound to achieve the systematic synthesis of polysialo ganglio-series gangliosides (Scheme 7). Glyco-sylation of GA2 acceptor 12 with a-sialyl-(2— 8)-sialic acid donor 13 in the presence of NIS-TfOH in acetonitrile at -25 °C, afforded the desired pentasaccharide in 50% and no P-isomer was isolated. De-O-isopropylidenation of the pentasaccharide with aqueous 80% acetic acid afforded the acceptor 14 in 91% yield. It is noteworthy that the key intermediate 14 was prepared by one step, de-O-isopropylidenation, after the construction of GD2 pentasaccharide, in contrast to the synthesis of GDI a. 

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